DESCRIPTION: Anchorage-dependent cells respond to matrix molecules by the formation of focal adhesions. These are sites of complex transmembrane signaling which impact cell behavior and growth, both through short term effects on cytoskeletal organization and longer term effects on gene transcription. The long term goal of this research is to understand the molecular mechanisms underlying focal adhesion formation and subsequent signaling role in migration, anchorage, and matrix assembly and turnover. Cell-matrix interactions have important roles in development and wound repair, and are altered in the pathogenesis of rheumatic diseases, tumorigenesis and fibrosis. Syndecan-4 is a transmembrane heparan sulfate proteoglycan that regulates focal adhesion assembly. Transfection studies show that a region of its cytoplasmic domain can influence focal adhesions, cytoskeletal organization, and migration. This region of syndecan-4, but not equivalent regions from the other three syndecan members, can directly bind protein kinase C and regulate its activity. Oligomerization of the core protein is required. This, and protein kinase C regulatory ability, are both augmented by syndecan-4 interactions with phosphatidylinositol 4,5 biphosphate (PIP2), known to be a regulator of actin filament and focal adhesion assembly. The proposed studies will determine: (1) whether protein kinase C, syndecan-4 and PIP2 form a ternary signaling complex in vivo, (2) the sites of interaction between these three cell membrane associated components and how this is regulated, (3) the roles of the ectodomain and cytoplasmic domain of syndecan-4 core proteins, and of its glycanation, in focal adhesion assembly, and (4) the pathway by which protein kinase C regulates focal adhesion assembly, possibly through convergence with other signaling cascades, such as G proteins of the Ras superfamily, lipid metabolism and tyrosine kinases. These studies will use a combination of physical, chemical, immunological and molecular techniques, and will serve as a basis for intervention in the controlling role of focal adhesion and cytoskeletal organization.